The present invention relates to an overlocking sewing machine, and more particularly to a looper changeover device for an overlocking sewing machine capable of forming overlocked stitches with one needle and two threads and one needle and three threads.
Conventional overlocking sewing machines for producing overlocked stitches with one needle and three threads include a sewing needle, a lower looper and an upper looper secured to a looper holder, which cooperate to form such overlocked stitches. Overlocking sewing machines for forming overlocked stitches with one needle and two threads have a sewing needle, a lower looper and a spreader, which are cooperatively actuatable to produce the described overlocked stitches.
Recently, a sewing machine was proposed in U.S. Pat. No. 4,237,804 for stitching fabric edges with an overlocked stitch with one needle and three threads, the sewing machine including an upper looper and a separate movable member attached thereto, which together define a hook portion for overcasting a fabric edge with one needle and two threads as with a single spreader. When forming overlocked stitches with one needle and three threads, the movable member is brought away from the upper looper to release the hook portion and allow the upper looper to function as intended. In this machine, the combined hook portion moves along the same path as that of the upper looper when forming overlocked stitches with one needle and three threads, so that the hook portion and the upper looper will meet a lower looper at the same position to produce the respective stitches. The separate movable member which is necessary to cooperate with the upper looper in providing the combined hook portion for formation of overlocked stitches with one needle and two threads must be retracted, when not in use, into a position in which the movable member does not interfere with operation of the sewing machine, and hence a space must be reserved for retracting the movable member therein. Furthermore, when the combined hook portion picks up a thread from the lower looper, the thread therefrom tends to be caught in a gap defined between the upper looper and the separate movable member.
Thus, the known overlocking sewing machines even with the combined hook portion upper looper and movable member, are unable to form overlocked stitches of the described two types, reliably and smoothly, while permitting the change between stitch types to be quickly made.
It is therefore an object of the present invention to solve the foregoing problems encountered with the prior apparatus by providing an improved looper changeover device which enables the production of both single needle, three thread overlocked stitches and single needle, two thread overlocked stitches upon cooperation with a needle and a lower looper in a sewing machine.
This object and other objects, features and advantages of the present invention will become apparent from the following description when considered in connection with the accompanying drawings.